Chinese patent ZL01807570.3 discloses an apparatus for separating particles from a fluid stream. Specifically, as shown in FIG. 1, the apparatus includes one upstream cyclonic separating device 10′ and a plurality of downstream cyclonic separating devices 20′ arranged in parallel with each other, and each downstream cyclonic separating device 20′ is at least partially extended into an interior of the upstream cyclonic separating device 10′. The apparatus for separating particles from the fluid stream generally has a large height, a large volume, and a low separation efficiency.